1. Field of the Invention
This invention relates to a method for manufacturing a semiconductor substrate that is generally used for a semiconductor device including a composite IC and an LSI.
2. Description of the Related Art
An SOI (Silicon On Insulator) semiconductor device has a semiconductor layer that is disposed on a semiconductor substrate through an intermediate insulating layer. Such an SOI substrate is suitably used for a device such as a composite IC, a high withstand voltage IC or an LSI for a portable instrument that is required to have high speed and low consumption power, in which several kinds of elements such as bipolar, MOS, and power elements are mounted on one chip.
To manufacture the SOI semiconductor device, an SOI substrate is required, which includes a high-quality crystalline semiconductor layer that is formed on a layer made of an insulating material such as SiO2 with extremely high resistance. Known conventional methods for manufacturing the SOI substrates include a bonding method, a SIMOX method, a method that combines bonding and ion implantation by utilizing hydrogen brittleness, and the like.
However, the SOI substrate manufactured by conventional techniques in any of the above-described methods is several to several dozen times more expensive than an ordinary bulk substrate. This is the biggest reason for preventing the SOI semiconductor device from being practically used, regardless of its inherent high performance and high functionality.
The present invention has been made in view of the above problems. An object of the present invention is to provide a method for manufacturing a semiconductor substrate suitably used for an SOI semiconductor device, with high quality at low cost.
Briefly, according to a first aspect of the present invention, after an epitaxial layer is formed on a semiconductor substrate, an insulating layer is formed by deposition at an interface between the epitaxial layer and the semiconductor substrate by performing a heat treatment in an oxidizing atmosphere. Thus, the semiconductor substrate for an SOI semiconductor device can be manufactured easily at low cost. A thickness of an SOI layer equired for the semiconductor device can be determined by he thickness of the epitaxial layer.
According to a second aspect of the present invention, n apparent SOI substrate can be formed by epitaxially growing a semiconductor layer on a semi-insulating substrate having a high resistance. Preferably, before the semiconductor layer is epitaxially grown on the substrate, a heat treatment is performed in a hydrogen atmosphere to improve crystallinity on a surface of the semiconductor substrate. Accordingly, the crystallinity of the semiconductor layer is further improved.
According to a third aspect of the present invention, a base wafer and a bonding wafer are prepared, one of which is composed of a semiconductor substrate containing oxygen at a high concentration or a semi-insulating semiconductor substrate having a high resistance. An oxide film is formed on one of the base wafer and the bonding wafer. Then, the base wafer and the bonding wafer are bonded together with the oxide film interposed therebetween. After that, a back surface of the bonding wafer at an opposite side of the base wafer is ground and polished to form an SOI layer on the base wafer through the oxide film.
According to fourth aspect of the present invention, first, an element is ion-implanted into a high resistance semiconductor substrate, containing oxygen at a high concentration, to form a deposition nuclear layer by the element. The deposition nuclear layer has a plurality of nuclei for deposition and extends at a depth from a surface of the semiconductor substrate. Then, a heat treatment is performed to the semiconductor substrate to form an oxide layer in the semiconductor substrate by making the oxygen, contained in the semiconductor substrate, deposit using the plurality of nuclei in the deposition nuclear layer.
According to the present invention described above, in any case, the semiconductor substrate for an SOI semiconductor device can be manufactured with high quality at significantly reduced low cost.